Just to answer my own question for people that come googling here.
Here is what you need to do if you want to make webrat work with Rails
3 and the regular rails (non-rspec, non-cucumber) test suite.
To your gem file add:
gem 'webrat', '>=0.7.2.pre', :git => '
http://github.com/kalv/
webrat.git'
To your testhelper.rb add:
include Webrat::Methods
include Webrat::Matchers
Leave config.mode = :rails, (don't use :rack), and make sure you have
git installed, obviously, then run bundle.
Cheers,
Jan
(Answer derived from the thread below that deals with Rails 3 and
Cucumber. I didn't have any luck with the orangewise fork mentioned
in the other thread.).